things that directly harm other taxpayers - murder, physical violence, theft, false slander/reputational attacks...

prohibiting things that harm the individual should not be the role of government, IMO. Government, in the liberal/Enlightenment tradition, is there as a protector of your 'rights' to life, liberty, and property. While it has a duty to protect you from things which could harm you (eg junk food/sugary drinks), it also has a duty to let you do what you choose to do, even if it's 'bad' for you (eg eat junk food and drink sugary drinks).

Hence the compromise - you can smoke cigarettes and drink Coca-Cola, but the makers of cigarettes and soft drinks have to warn you beforehand, and the transaction may be more taxed than things like basic foods.